Test systems are critical to the manufacture and maintenance of modern electronic devices and systems including, but not limited to microwave devices, cell phones, telecommunication and computer networks, and television transmission equipment. Some examples of such test equipment are scalar network analyzers, vector network analyzers, spectrum analyzers, and power meters. Most of these test systems may be calibrated to mitigate or remove the effects of any test system imperfections from a measurement of a device under test (DUT). Such calibration uses the test system to measure a calibration standard. A calibration standard is simply a DUT having known performance characteristics. The test system is calibrated using differences between the known performance characteristics of the calibration standard and measured results obtained from measuring the calibration standard.
In many situations, a test fixture is used to facilitate testing a particular DUT by the test system. The test fixture essentially interfaces the test system to the DUT. In some situations where a test fixture is employed, calibrating the test system to include effects of the test fixture is either difficult or impractical. In other situations, the DUT simply may be specified in terms of performance in a given test fixture (e.g., a reference test fixture). In either case, the test system may be calibrated at an interface between the test fixture and the DUT, such that error-corrected measurements of the DUT in the test fixture include both an actual performance of the DUT and a performance of a reference test fixture. Subsequent copies of the DUT may be compared and evaluated relative to an original DUT by testing each copy in the reference test fixture.
Unfortunately, the reference test fixture may not be well suited for use in production testing during a mass production of the DUT. Instead, a production test fixture, adapted for high-speed production testing, for example, may be employed. Since the production test fixture differs physically from the reference test fixture, the production test fixture typically has different performance characteristics from those of the reference test fixture. As such, calibrating the test system at inputs of the production test fixture will generally yield different measured results for a given DUT than would be obtained if the DUT were to be tested in the reference test fixture. The differences in measured results between the reference fixture and the production fixture can lead to incorrect production test results, such as failing DUTs that are actually operating properly or passing DUTs that are not operating within acceptable tolerance limits, simply because the text fixture differences obscure a true performance of the DUTs.
Accordingly, it would be advantageous have a way to correct a calibration of a test system for measuring DUTs in different test fixtures and/or to correlate measurements of the DUTs taken with the test system in different test fixtures. Such a correction and/or transformation would solve a long-standing need in the calibrated test systems using multiple test fixtures.